Cooling system



y 4, 1948- G. CAMILLI ET! AL 2,440,930

COOLING SYSTEM Filed April 2, 1945 cmcccccac'cccaco llllll d wniiiillIiii Inventors; Guglielmo Camilli, Harry E Miller; y flit/W76? TheirAtborh evL Patented May 4,1948

COOLING SYSTEM Guglielmo Camllll and Harry 1'. Miller, Pittsfleld, Masa,assignors to General Electric Company, a New York corporationApplication April 2, 1945, Serial No. 588,170

6 Claims. (Cl. 62-115) This invention relates to cooling systems andmore particularly to improvements in cooling systems for encased liquidinsulated stationary electromagnetic induction apparatus.

Typical examples of such apparatus are power transformers and notinfrequently such power transformers must be placed in locations wherespace is at a premium. Examples of such locations are locomotives andcongested industrial load center areas. It is customary to cool suchtransformers by means of a radiator or radiators mounted outside thetank and through which the dielectric liquid circulates. In this mannerthe dielectric liquid also acts as a coolin medium. Obviously, the sizeof the power transformer can be reduced by reducing the area of theradiator or heat exchanger, but if this is done, the tennperature' ofthe cooling liquid must increase in order to dissipate the same amountof heat which is generated in the transformer. Unfortunately, the mostsatisfactorily known dielectric liquids, such as mineral oils andaskarels, do not have a high stable temperature so that heretofore therehas been a definite limit on the minimum size of the cooling radiator.

In accordance with this invention a second liquid is employed forperforming the refrigerating function so that the dielectric liquid willperform essentially only its prime function of acting as an insulator.By making the refrigerating liquid one which is stable at relativelyhigh temperatures and which has a lower boiling point than thedielectric liquid it is possible by means of mechanical refrigerationcycle to operate the radiator at greatly increased temperature risesabove that of the ambient, which normally is air, and in this manner thesame amount of heat can be dissipated in a much smaller radiator. Itwill be noted, however, that this high temperature is outside thetransformer tank and therefore does not reduce the life of thetransformer.

Another feature of the invention is that the refrigerating liquid ispreferably introduced directly into the dielectric liquid in what may becharacterized as a spray. This produces turbulence in the dielectricliquid which not only facilitates the cooling of the dielectric liquidbut at the same time prevents it from congealing or even freezing solid.This is important, for if the viscosity of the dielectric liquidincreases materially, its circulation. decreases so that heat will notbe drawn away from the heat evolving electrical apparatus as rapidly asnecessary and injurious hot spot temperatures will result.

An object of the invention is to provide a new and improved coolingsystem.

Another object of the invention is to provide a new and improved coolingsystem for liquid insulated encased electrical apparatus.

A further object of the invention is to reduce materially the size ofthe external cooling area of a power transformer.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

In the drawing Fig. l is a front elevation of a power transformerembodying the invention and Pig. 2 is an enlarged cut -away sideelevation of the transformer shown in Fig. 1.

Referring now to the drawing and more particularly to Fig. 1, there isshown therein a power transformer having a tank l and having an exteriorcooling unit 2. The cooihig unit 2 consists principally of a radiator orheat exchanger 3 and a housing t for auxiliary apparatus. it will henoted that the size of the radiator 3 in comparison with the size of thel is very much smaller thanin conventional transformers.

Referring now to Fig, 2, the tank l contains the core 5 and the coils 8of a transformer. i'hese parts are completely immersed in any suitabledielectric liquid l which part ally fills the tank up to the level 13.Examples of suitable dielectric liquids are mineral oil and aslsarel.

Mixed with the dielectric liquid 2' is a refrigerating liquid, of anysuitable type, such as dichlcromonofluoromethane (Cli f/1215 which has alower boiling point than that of the dielectric liquid l and whichboiling point is, in fact, lower than the normal operating temperatureof the dielectrio liquid i so that the refrigerating liquid vaporizesinto vapor hubhles within the dielectric liquid 1 and which bubbles riseto the top of the dielectric liquid. This refrigerating liquid is alsostable at very much higher temperatures than the dielectric liquid sothat its vapor can be compressed to relatively high pressures and termperatures and then recondensed into a liquid without changing itschemical properties. The vaporization of the refrigerating liquid, ofcourse, isothermally removes heat from the dielectric liquid 1.

Heat is removed from the vaporized refrigerating liquid by drawing itout of the space above the dielectric liquid level 8 through a conduit10 by means of a compressor I I. This compressor may be driven in anysuitable manner, such as by an electric motor H. The compressor raisesthe pressure and consequently the temperature of the refrigerant gas torelatively high values;

for example, the temperature can be raised to 200 degrees Centigradeabove the temperature of the surrounding air. This high temperature gasis then discharged through a conduit l3 into the radiator 3. Preferably,motor-driven fans M are provided for forcing air through the radiator 3so as to increase" the'heat dissipating capacity of the radiator. Byreason of the high temperature of the refrigerant gas which enters theradiator 3 a relatively large amount of heat can be dissipated by aradiator of relatively small size for it is well known that the amountof heat exchanged in a radiator is a function of the temperature rise ofthe fluid to be cooled over the ambient temperature. The refrigerant isisothermally condensed at high temperature into a liquid in the radiator3 and it then fiows under pressure through a conduit it into the tank Inear the bottom where it emerges through nozzles I 8' in the form of thesprays indicated schematically at H. An expansion device which, forexample, may be in the form of a regulating valve I5 controls this flow.

The temperature of the vaporizing liquid sprays I! is very much lowerthan the temperature of the dielectric liquid 1 but the sprays causeturbulence in the dielectric liquid 'l and thus not only increase theeffective contact area between the two liquids and thus increase theheat exchange between them and the vaporization of the refri eratingliquid but this turbulence also effectively prevents congealing orfreezing of the dielectric liquid.

For preventing the gas bubbles 9 from coming in contact with thetransformer core and coils suitable barriers or bailles I8 are providedand, as shown, these have openings i9 near the bottom and they do notextend to the top of the dielectric liquid, with the result that thereis a circulatory motion of the dielectric liquid, as shown by thearrows. Thus, the cooled dielectric liquid between the barriers and thewalls of the tank 9 increases in density and descends, thus displacing Ithe warmer dielectric liquid at the bottom which flows through theopenings l9 between the barrier and upward between the barrier and coreand coils, and this circulation further improves the heat conductionaway from the core and coils.

The system may be automatically controlled in any suitable manner, suchas by means of a thermal relay 20 having a temperature responsivecontrol bulb 2| which is immersed in the top dielectric liquid. Thethermal relay can be set to start the compressor motor l2 and the motorsfor the fans I4 whenever the temperature of the dielectric liquidreaches a predetermined maxi mum value and this relay will then shutoil. these units when the temperature is reduced sufliciently below thisvalue.

While there has been shown and described a particular embodiment of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications can be made therein without departing from theinvention and, therefore, it is aimedin the appended claims to cover allsuch changes and modifications as fall within the true spirit and scopeof the invention.

What we claim as new and desire to secure by Letters Patentof the UnitedStates is:

l. A cooling system for an enclosed space comprising, a'first liquidpartially filling said space, said first liquid having a relatively highboiling point and a relatively low maximum stable tempansion .device fordischarging condensate of said second liquid directl into said firstliquid.

2. A cooling system for an enclosed space comprising, a first liquidpartially filling said space, said first liquid having a relatively highboiling point and a relatively low maximum stable temperature, a secondliquid mixed with said first liquid, said second liquid having arelatively low boiling point, and a relatively high maximum stabletemperature, the normal operating temperature of said first liquid beingabove the boiling point of said second liquid a condenser outside saidspace, a compressor for drawing vapor of the second liquid out of thespace above the level of the first liquid and discharging it atsubstantially increased pressure and temperature pressor so asautomatically to maintain the ternperature of said first liquid below apredetermined value.

3. A cooling system for electrical apparatus comprising, a casing, heatevolving electrical apparatus within said casing, a dielectric liquidpartially filling said casing and surrounding said apparatus, arefrigerating liquid mixed with said dielectric liquid, the normaloperating temperature of said dielectric liquid being above the boilingpoint of said refrigerating liquid, a condenser outside of said casing,a compressor for drawing vapor of the refrigerating liquid out of thespace above the level of the dielectric liquid and discharging it atsubstantially increased temperature and pressure into said condenser,and means including an expansion device for discharging condensate ofsaid refrigerating liquid directly into said dielectric liquid. I

4. A cooling system for electrical apparatus comprising, a casing, heatevolving electrical apparatus within said casing, a dielectric liquidpartially filling said casing and surrounding said apparatus, arefrigerating liquid mixed with said dielectric liquid, the normaloperating temperature of said dielectric liquid being above the boilingpoint of'said refrigerating liquid. a condenser outside of said casing,a compressor for drawing vapor of the refrigerating liquid out of thespace above the level of the dielectric liquid and discharging it atsubstantially increased temperacoming into contact with said electricalapparatus.

5. A small area cooling system for stationary electromagnetic inductionapparatus comprising,

a tank, stationary electromagnetic induction apparatus inside said tank,a dielectric liquid partially filling said tank and surrounding saidelectromagnetic induction apparatus, said dielectric 5 liquid having'arelatively high boiling point and a relatively low stable temperature, arefrigerat ing liquid mixed with said dielectric liquid, saidrefrigerating liquid having a relatively low boiling point and arelatively high stable temperature, the normal operating temperature ofsaid dielectric liquid being above the boiling point of saidrefrigerating liquid, a relatively small area condenser outside of saidtank, a compressor for drawing liquid out of said tank above the levelof the dielectric liquid and discharging it at sub stantially increasedpressure and temperature into said condenser, and means including anexpansion device for discharging condensate of said refrigerating liquiddirectly into said dielectric liquid.

6. A dielectric liquid immersed encased transformer, a radiator outsidethe transformer casing, said radiator having insuflicient area fordissipating the heat of said transformer if said dielectric liquid iscirculated therethrough at any stable temperature thereof, means forcooling said transformer comprising a refrigerating liquid in heatexchanging relation with said dielectric liq- .uid, a compressor forforcing vapor or said re- REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 146,620 Twining Jan. 20, 1874513,421 Rowland Jan. 23, 1894 1,669,918 Streeter May 15, 1928 Gay Feb.5, 1929

